The invention relates to an aerofoil assembly and a method of assembly of an aerofoil assembly.
Aerofoil assemblies such as stages of a gas turbine compressor or turbine typically have an array of blades 10 which are located in a supporting disc or drum 12 and have a damping member 14 disposed between the blades 10 in order to achieve a desirable vibration characteristic. Such an arrangement is shown in FIGS. 1 to 3 (PRIOR ART) in which the damping member 14 is located in a compartment 16 formed between adjacent blades 10.
The damping member 14, as viewed in FIG. 1, has a “cottage roof” type cross section in that it is part triangular (or “peaked”). As shown in FIGS. 2 and 3 (PRIOR ART), which are sectional views on arrow “A” in FIG. 1 (PRIOR ART) the damping member 14 is largely rectangular in cross section. As also shown in FIG. 2 (PRIOR ART) the compartment 16 is formed by the provision of a recess 18 in each blade 14, and a shelf 20 at either end of the recess 18 forms a support structure 22 for the damping member 14. The member 14 is trapped in the compartment 16 by the shelves 20 since the overall span or longitudinal length “x” of the damping member 14 is greater than the distance between edges 24 of the shelves 20. As shown in FIG. 3 (PRIOR ART) part of the method of assembly requires at least one of the blades 10 to be slid out of the array to allow for a locking member 26 to be inserted in a groove 28, on the rear or forward edge of the blade, in direction B. Thus the damping member 14 must be small enough to allow the blades 10 to move relative to one another to allow access to the groove 28, and yet the damping member 14 must be long enough to stay trapped between the blades 10 when the blades 10 are realigned. Manufacturing tolerances may result in the damping member 14 or support structure 22 being undersize and hence the damping member 14 may fall out. In this eventuality damage may be caused to the blade disc 12 and other components it comes into contact with.